M.V. Diamanti, L.G. Bettini, P. Milani, M. Sansotera, F. Persico, W. Navarrini, M.P. Pedeferri
Politecnico di Milano,
Keywords: advanced oxidation processes, nanopowders, immobilization, fluoropolymeric coating, TiO2
Summary:The use of nanosized photocatalytic TiO2 in suspension or slurry type reactors is well reported. However, the industrial feasibility of such systems is limited, on account of the low quantum efficiency reported for slurry processes and of the need for a post-treatment catalyst recovery stage, which may present poor efficiency, with the double drawback of dispersing nanoparticles in the environment and losing precious photocatalyst. In this work, the photodegradative activity of titanium dioxide immobilized into a multilayered transparent fluoropolymeric matrix has been studied. Several TiO2 nanostructured powders featuring different primary particle size, crystalline phase and specific surface area have been produced by the flame spray pyrolysis (FSP) of organic solutions containing titanium (IV) isopropoxide. The activity of such powders has been tested and compared to that of TiO2 P25 by Evonik Degussa, which is the reference nanopowder commonly employed in the evaluation of the photocatalytic activity of non-commercial TiO2. A multilayer ionomeric-perfluorinated matrix has been used to immobilize the powders, having high chemical resistance and transparency towards UV light, good permeability to oxygen and good wettability to favor interactions with the polluted aqueous solutions. Results show that the TiO2 P25 containing coating has higher photocatalytic activity in degrading organic dyes than dispersed TiO2 P25, particularly at low pollutant concentration. Further tests, conducted in presence of a solid suspension, prove the photoactive coating to be effective even in turbid solutions. In addition, TiO2 is not deactivated by slime interposition between the UV source and the pollutant. Tests have been then repeated on coatings containing TiO2 nanopowders produced by FSP: apparent pseudo-first order kinetic constants show an increase in photocatalytic efficiency from 40% to 100% depending on powders particle size. In conclusion, the research presented proves the possibility to achieve highly efficient water purification by immobilizing TiO2 nanopowders in a suitable polymeric coating, avoiding any costly separation of the catalyst from the purified water; moreover, the nanostructured TiO2 powders produced by FSP demonstrate a large improvement in photocatalytic activity compared with reference P25.